There are several interesting design ideas that have taken hold.
The Hero Shot / One-Page Design / Flat-UI Design
The Hero Shot
A hero shot is a large image that dominates the viewing area. The image, for all practical purposes, is the design. It's a very clean, very engaging look. The image brings out the emotional response of the viewer and the simple navigation and call-to-action elements do not overwhelm the viewer. Present different images on reload and the site remains fresh for return users - and it also allows one to more easily integrate multi-variate testing into site design.
One Page Design
The hero shot works very well with one page design. There were many reason we, as designers, went away from one page design in the late 1990s. Multi-page designs were "kooler"; it allowed for more images and text to be quickly shown to the user (connection speeds were MUCH slower then); it allowed for knowing when and where the user dropped out; it was useful for breaking up server-side interaction; it was useful for showing more advertising; it allowed more methodical presentation of data; and it was kooler. Designers and marketers want something new, attractive.
As with all things fashion the one-page design is fresh once again. Of course there's some interesting twists: namely the transitions between "pages." For all practical purposes the one-page design is presenting differing "screens" with transitions between them, but the fact that they're all on one page makes it new. I would say that there is also a utility in the design as all the information is loaded and remains even if the server connection is lost. Ultimately its appeal is not its utility - it's its freshness. Regarding the reasons why designers went away from one-page design and their return. All the practical reasons that existed before no longer remain.
The use of flat, as opposed to textured, or beveled elements. It's advantage is that it has a clean, fresh look. It allows more elements to be presented to the user but at the same time maintain a more minimalist feel.
All three elements are part of the current design zeitgeist where mobile design is influencing design presented on larger screens.
* For my distinction between Web Design, UX Design and UI Design please see "What's in a Name? Web, UX, UI Design"